High strength corrosion resistant nickel-base alloy

ABSTRACT

Alloys containing controlled percentages of chromium, aluminum, titanium, molybdenum, tungsten, tantalum, zirconium, boron, carbon and a dispersoid such as yttria afford good stress rupture properties at intermediate temperatures, e.g., 1400*F., and at more elevated temperatures, e.g., 1900*F., together with good oxidation and/or control of nitrogen important for enhancing sulfidation resistance.

United States Patent [1 Benjamin et al.

1 HIGH STRENGTH CORROSION RESISTANT NICKEL-BASE ALLOY [75] Inventors:John Stanwood Benjamin; Jay Ward Schultz, both of Suffern, NY.

[73] Assignee: The International Nickel Company,

Inc., New York, NY.

[22] Filed: Aug. 28, 1974 [21] Appl. No.: 501,052

Related US. Application Data [63] Continuation-impart of Ser. Nos.375,530, July 2, 1973, abandoned, and Ser. No. 302.201, Oct. 30, 1972,abandoned,

[52] US. Cl. 29/1825; 75/.5 R; 75/.5 BC;

75/122; 75/171 [51] Int. Cl. C22C 29/00; C22C 19/05 [58] Field of Search75/.5 BC, .5 BB, .5 BA,

[56] References Cited UNITED STATES PATENTS 3,591,362 7/1971 Benjamin75/211 X Dec. 16, 1975 Benjamin 29/1825 Benjamin 75!.5 BC

Primary Examiner-L. Dewayne Rutledge Assistant ExaminerArthur J. SteinerAttorney, Agent, or Firm-Raymond .1. Kenny; Ewan C. MacQueen [57]ABSTRACT 12 Claims, No Drawings HIGH STRENGTH CORROSION RESISTANTNICKEL-BASE ALLOY The subject application is a continuation-in-part ofapplication Ser. Nos. 375,530 filed 7/2/73 and 302,201, tiled 10/30/72both of which are now abandoned.

The present invention is directed to the so-termed superalloys, andparticularly to precipitation harden able, dispersion-strengthenednickel-base alloys capable of operating exceptionally well at bothintermediate and elevated temperatures and under corrosive conditions.

By reason of the many advances in aircraft design, the metallurgicalcommunity has been under a continuous challenge to develop alloyscapable of withstanding the more severe service conditions inherentlyimposed, notably increased speeds at higher temperatures and greaterload-bearing capacities. In recent years, primary emphasis has probablybeen addressed to performance characteristics at the more elevatedtemperature levels, to wit, 1700-2000F. There are, however, thosecomponents of which more is demanded witness, for example, the blades ofa gas turbine engine. As is known, different sections of the blades areexposed to completely different combinations of temperature and stress.In this regard, the outer portions of the blades operate at temperaturesupwards of 1700F. whereas the platform portion closer to the axis of theengine might operate at temperatures on the level of l200 to 1400F., butthe latter is subjected to tremendously greater stress due to thecentrifugal nature of the loading in a rotating part.

The fact that an alloy might respond favorably at the higher temperatureplateaus, does not invoke the corollary that it is also capable ofperforming satisfactorily at temperatures on the order of 12001400F. Theproduct known as TD nickel has fairly good strength at the hightemperatures but manifests a distinct propensity to undergo prematurecreep at the intermediate temperature levels.

The problem becomes somewhat compounded where excellent resistance tocorrosion, particularly oxidation and/or sulfidation, is of necessity.For as we have found a given alloy may display acceptable values interms of stress rupture characteristics at temperature only to suffer apronounced susceptibility to corrosive attack.

The thrust of the subject invention is, accordingly, to bring togetherin one alloy the capability of delivering outstanding stress rupturestrength at both intermediate (1400F.) and elevated (1900F.) temperaturelevels and good resistance to oxidation and/or sulfidation. In thisconnection and insofar as we are aware, the subject alloys afford thehighest combination of strength and corrosion resistance known in thesuperalloy art.

Generally speaking, alloys contemplated in accordance herewith contain(weight percent) about 13 to 17%, e.g., 13.25 to 16.25%, chromium; about2.5 to 6%, e.g., 2.75 to 5.25%, aluminum; about 2 to 4.25% titanium, thesum of the aluminum plus titanium being preferably at least about about1.75 to about 4.25% or 4.5% molybdenum; about 3.75 to about 6.25%tungsten; up to 4%, e.g., up to 3%, tantalum, about 0.02 to 0.5%, e.g.,0.05 to about 0.175%, zirco nium; about 0.001 to 0.025% boron. a smallbut effective amount, e.g., 0.2% or 0.5%, and up to about 2% of 2yttria; up to 0.2% and advantageously not more than 0.125% carbon; andthe balance essentially nickel.

Within the foregoing ranges, where the emphasis is on oxidationresistance as well as stress-rupture strength, the alloys should containat least 3.5% aluminum. 13.75% or more of chromium and not more thanabout 3% titanium. 1n striving for the optimum by way of resistance tosulfidation then the percentages of aluminum, titanium and tungstenshould be correlated such that the aluminum is from 2.75% to 4.6%, thetitanium is at least 2.4% and the tungsten is at least 4.75%, the sum ofthe titanium plus tungsten benefcially being at least 7.75%. For bothoxidation and sulfidation resistance coupled with high strength thealloys should contain about 3.5 to 5.25% aluminum, about 13.75 to 16.25%chromium, about 2.4 to 3% or 3.25% titanium, and from about 4.75 to6.25% tungsten, the other constituents being within the ranges firstgiven.

In terms of the individual alloying constituents, it would appear that anumber of interactive or conflicting forces are involved, theirrespective roles being difficult to delineate at best. Seemingly, theseinteractions are particularly pronounced in respect of both oxidationand sulfidation resistance. For example, chromium, titanium and tungstenimpart a most potent effect in achieving optimum resistance tosulfidation. By the same token, titanium and tungsten, for example, tendto detract from 1900F. stress rupture strength, although not at 1400F.Chromium and aluminum are indispensible in conferring resistance tooxidation yet aluminum at 1900" is deemed somewhat detrimental whereaschromium impairs stress-rupture properties at both 1400 and 1900F. Suchconsiderations are indicative of the careful balance of chemistryrequired. Indeed, this balance is further required to develop a propergrain structure as detailed more fully herein.

With regard to yttria, it confers high stress-rupture strength,particularly at the higher temperature levels (1900F.). A small amountof this constituent, e.g., 0.4%, is effective in imparting this benefit,though it is preferred that about 0.5 to 1.5% be present. Percentages ofyttria above 2% are unnecessary. Tantalum enhances strengthcharacteristics especially in the 1200l400F. Temperature region. From1.5 to 3% of this element is deemed beneficial.

1n referring to nickel as constituting the balance" or balanceessentially in respect of the above composition, the presence of otherelements in amounts which do not adversely affect the basiccharacteristics of the alloys is not excluded. In this connection, thealloys may contain up to 3% columbium (although they are preferablycolumbium free); up to 10% cobalt; up to 3% hafnium; up to 0.75% or 1%oxygen; up to 3% iron (as a contaminant); and up to 0.3% nitrogen. Butit is most preferred, as will be shown hereinafter, that nitrogen notexceeded about 0.1% particularly in seeking the optimum of sulfidationresistance. Cobalt has a negative efiect at 1900F. and should, ifpresent, he held to less than 8%. In addition, while yttria is very muchpreferred as the added dispersoid constituent, other refractorydispersoids, e.g., thoria and lanthana, can partially replace or be usedin lieu thereof where a lesser combination of overall properties can betolerated. Other refractory dispersoids can be present aside from theaforementioned yttria, lanthana and thoria, including the oxides,carbides. borides, and nitrides (provided the total nitrogen contentdoes not exceed about 0.1%) of one or more materials such as thorium,zirconium, hafnium, titanium and oxides of aluminum, yttrium, lanthanum,cerium, etc. It is to be also understood that a given range for aparticular element of the alloys can be used with a given range for anyother element.

In carrying the invention into practice, the alloys should be producedby the mechanical alloying process as described in US. Pat. No.3,591,362 and incorporated herein by reference. As is known, mechanicalalloying involves the dry, intensive high energy milling of a powdercharge whereby the initial powder constituents are simultaneouslyfragmented and cold bonded to provide a homogeneous, intimateinterdispersion of alloying elements in the form of composite particlescorresponding to the alloy composition desired. In this connection, theimpacting elements used are preferably hard and impact resistant such asthrough hardened 52100 steel. Using a 4 gallon attritor mill, forexample, a ball-to-powder ratio of about 15:1 to 25:1 by volume ispreferred, the impeller speed being suitably conducted over the range of250 to 300 rpm for a period of about 12 to 24 hours. For processing in agal. attritor a speed of 150-200 rpm can be used, a period of 15-40hours being satisfactory. Larger attritors permit of reduced impellerspeeds.

Subsequent to mechanical alloying the composite alloy product particlescan be compacted as by hot extrusion. A temperature of about 1800 to2125F. is

of the processing, a dynamic atmosphere of air and nitrogen wassupplied. 1n the case of Alloy A, 16 cc per minute of air and 400 cc perminute of nitrogen were used whereas for Alloys B and C 12 and 9 cc ofair was employed, the amount of nitrogen being the same.

The coarsest 5% of the powders was removed, the remainder being packedin 3% inch diameter mild steel cans, sealed, heated to 1950F. and thenextruded through dies (0.75 inch for Alloy A and 0.875 inch for Alloys Band C) using glass and grease as a lubricant. An extrusion speed ofapproximately 3 to 4 inches per second was measured.

The alloys were then subjected to a germinative grain growth treatment(secondary recrystallization) consisting of heating for one half hour at2300F. for Alloys A and B and 2250F. for Alloy C. After aging at 1550F.for approximately 24 hours, microstructural examination revealed thatthe alloys exhibited a desired coarse grain structure elongated in thedirection of extrusion.

Each of the three alloys was then stress rupture tested at both 1400F.and 1900F. and also tested for cyclic oxidation and sulfidationresistance. The oxidation test was conducted at 1100C. for 500 hours,the alloys being cycled to room temperature each 24 hours. A cruciblesulfidation test was used and this comprised partially immersing a 300mil diameter specimen of each alloy in a 90% Na SO 10% NaCl saltsolution, the test being conducted at 1700F. The analyzed comitions andresults of the various tests are reported in suitable and an extrusionratio of about 10:1 25:1 is Tables 1 [[1 below TABLE 1 COMPOSITION Cr AlTi Mo w v 0, Zr B Fe 0 N Alloy m 13.9 4.8 2.4 3.7 3.9 1.1 0.1 0.005 1.10.58 0.16 B 13.5 4.2 3 4 s 1.1 0.15 0.01 0.7 0.5 0.14 c" 15.0 4.5 2.753.5 5.5 1.1 0.15- 0.015 1.6 0.67 0.17

contained 2.4% tantalum "nominal composition plus 2.5% tantalum balancenickel and impurities quite satisfactory. Thereupon, the extruded piececan T LE [I be hot worked if desired.

ES PT RE D It is most importan t thatthe alloys then be treated to Testi E S 38 9 a}: H RR develop a germinatlve grain growth such that amicro- Alloy ps Hrs. 7: structure is produced characterized by coarseelon- A 900 25900 10.3 2.4 u gated grains having a high aspect ratio,e.g., 2:1 to 900 20.000 113.3 2.4 2.4 upwards of 100:1 This comprisessubjecting the alloys Q 32% gg:% 1%; a; :2 to a heat treatment withinthe temperature range of 1400 35,000 37.2 2.4 3.5 approximately 2125 toabout 2300F. If lower temper- C fg-ggg. 33- a atures are used such as onthe order of 2100 F., the 1400 75,000 1m alloys will retain the finegrain of the extruded structure 1400 35-000 0 8 and this is undesirable.On the other hand, should the .calcumd temperature appreciably exceed2300F., then incipient liquation will develop and this is alsoundesirable. Following this treatment within the temperature range TA LE"I of about l250 to 2000F., beneficially from 1450 to CORROSON DATA1600F., for a period of from about 16 to 30 hours. D OxidationSulfidation The following will serve to illustrate various aspects Alloyi AT of the invention. a

A series of three alloys were prepared, Alloys A, B Q and C, Table l, bymechanical alloying. The charges, c 500 13 rug/cm 100 21 which consistedof both elemental and master alloy powders, were placed in a 4 gallonattritor containing about 162-163 pounds of 5/16 inch diameter throughhardened steel balls. The charges were processed for about 16 /2 hours,the impeller speed of the attritor being maintained at about 288 rpm.During the course With regard to the above data, it will be observedthat Alloy A exhibited a stress rupture life of well over hours at1900F. under a stress of 20,000 psi. At 1400F. it similarly displayed astress rupture life above 100 hours notwithstanding the exceptionallyhigh stress level of 80,000 psi. Moreover, it underwent only a weightloss of but 11 mg/cm This is deemed to be outstanding in terms ofresistance to oxidation, particularly at the strength levels involved.Resistance to sulfidation, comparably speaking, was not as good as itmight otherwise be since the alloy underwent a loss of approximately 80mils during the period of test. By maintaining the total content oftitanium plus tungsten over 7.75, e.g., about 8.25%, sulfidationresistance would be enhanced. This is reflected by Alloy B which showeda remarkably low loss less than 30 mils; however, its susceptibility tooxidation was on the high side, this in part being a reflection of hightitanium. In contrast, Alloy C had excellent resistance to bothoxidation and sulfidation attack in combination with good stress ruptureproperties. Over an exceptionally severe sulfidation test period of 300hours, Alloy C corroded virtually completely with Alloy B still showinga loss of less than 30 mils.

As above-indicated, it is to advantage that the alloys be produced bymechanical alloying. In this connection and at least until recently,mechanical alloying was conducted in the presence of a dynamicatmosphere largely, if not completely, comprised of an oxygennitrogenmixture. However, such an environment has been found causative ofcertain problems in respect of both non-dispersion and dispersionstrengthened alloys of the superalloy type. In this connection, andgiven the benefit of retrospective review, scant attention was given tothe role of nitrogen in the composite particles produced, probablybecause the retained amounts thereof, being on the order of 0.l5-0.2% orso, were quite low (in contrast to oxygen) and were likely consideredinconsequential. In any case and irrespective of what transpiredheretofore, we have found that nitro gen, rather than being passive orinnocuous, can exercise a most detracting influence.

The difficulty can be minimized by recourse to utilization ofnon-nitrogen atmospheres. This notwithstanding, nitrogen can nonethelessbe introduced through the raw materials used, preprocessing procedures,the occurrence of leaks during the mechanical alloying process itself,etc. Moreover, and still important, nitrogen can lend to the efficiencyof the mechanical alloying process. Thus, its specific contemplated usecannot be overlooked. But the point of concern is that it does 6tageously not exceed 0.1% in mechanically alloyed" superalloys.

However, what we were unaware of (as is demonstrated herein) was that anotherwise small percentage of nitrogen, e.g., 0.15%, could subvertresistance to sulfidation. Furthermore, it now appears that bycontrolling the nitrogen content lower titanium and tungsten levels canbe used for a sulfidation resistant alloy. This, in turn, offers theprospect of improving elevated stress-rupture strength.

The following description and data is given as illustrative of what canbe accomplished in accordance herewith in terms of further improvedsulfidation resistance.

A series of alloys were prepared (compositions given in Table 1V) bymechanical alloying using both elemental and master alloy powders placedin a 4 gallon attritor containing about 162-163 pounds of 5/ 16 inchdiameter through hardened steel balls. The charges were processed forabout 16% hours, the impeller speed of the attritor being maintained atabout 288 rpm. During the course of the processing a dynamic atmosphereof air and nitrogen was supplied for three of the alloys, but thenitrogen was largely replaced by argon in each of the other alloys(argon 2%. 0 being used in two instances and argon plus 0.25% oxalicacid in the other, where the first percentage refers to gas volume andthe second to the weight of the powder charge).

The coarsest of the powders (approx. 5%) was removed, the remainderbeing packed in 3 inch diameter mild steel cans, sealed, heated to1950F. and then extruded using an appropriate lubricant. The alloys werethen subjected to a gerrninative grain growth treatment (secondaryrecrystallization) generally consisting of heating for one half hour at2250F. or 2300F. which was followed by aging at 1500F. for approximately24 hours.

Each of the alloys was then subjected to a crucible sulfidation testinvolving partially immersing a 300 mil diameter specimen of each alloyin a Na SO, 10% NaCl salt solution, the test being conducted at 1700F.for a time period as given in Table IV. The alloys were also tested forcyclic oxidation and this involved an exposure to air at 1 C. for 500hours, the alloys being cycled to room temperature every 24 hours.

TABLE IV sulfidation Oxidation Composition by Weight Time Loss Max lossAlloy Al Ti Ta Cr Mo W Zr B C Fe Y203 0, N (Hrs) (Mils) Attack Descaled(Mils) (mg/cm) D 3.7 2.3 2.0 14.0 4.0 4.0 .15 0.1 .074 1.6 1.1 .52 .14100 300 300 10 E 3.5 23 2.0 14.0 4.0 4.0.15.0] .075 2.1 1.1 .76 .071 30067 79 19 300 27 42 38 C 4.5 2.75 2.5 15.0 3.5 5.5 .13 .015 .069 1.6 1.1.67 .17 100 21 28 13 Argon 2'1 0., "Argon (25% oxalic acid added topowder) not require much nitrogen to impair one or more alloycharacteristics, for example, corrosion resistance. In accordanceherewith, the nitrogen level should advan- With regard to the abovedata, Alloys D and E are substantially the same in terms of compositionexcept for nitrogen content, the former having a nitrogen level twicethat of the latter. Alloys C and F are also similar 7 compositionallyexcept the respective percentages of nitrogen. Alloys G and H are alsodifferent largely by reason of molybdenum and tungsten contents.

In comparing Alloys D and E, low nitrogen Alloy E survived the severe300-hour sulfidation exposure whereas Alloy D had already manifestedvirtually total disintigration upon an exposure of but 100 hours. Whileit is difficult to think that such a small difference in nitrogen wouldbee causative of such a marked disparity in results, Alloys C and F andeven Alloys G and H rather confirm this phenomenon.

it is further noteworthy of mention that Alloy E withstood the 300-hourtest notwithstanding that the alloy contained but 23% titanium and 4%tungsten. As indicated, above 2.4% titanium and 4.75% tungsten should bepresent in the alloys for optimum resistance to sulfidation. This isdeemed beneficial for as also previously indicated, reduced titanium andtungsten levels would be expected to promote enhanced stress-rupturestrength at the more elevated temperatures, such as 1900F.

With regard to the remarkably low sulfidation loss of Alloy No. H (3 to4 mils), it is considered that this was due to the low molybdenumcontent in addition to the reduced percentage of nitrogen, the tungstenbeing but 4.2%.

The controlled use of low nitrogen levels, i.e., not greater than 0.1%and advantageously less than about 0.075%, is deemed applicable to notonly the range of mechanically alloyed superalloys described herein, butalso to such superalloys as those containing up to 65%, e.g., 2 to 35%,chromium; at least 1% of a hardening constituent from the groupconsisting of up to about or e.g., 0.5 to 8%, aluminum; up to about 10or 15%, e.g., 0.5 to 8%, titanium, and up to 15 or e.g., 0.5 to 10%,columbium; up to e.g., 0.5 to 12 or 15%, molybdenum; up to 20 or 25%,e.g., up to 3%, tungsten; up to 20%, e.g., 1 to 10%, tantalum, up to 2or 3% vanadium; up to 15%, e.g., up to 2 or 3%, manganese; up to l or2%, e.g., up to 0.5 or 1%, carbon; up to l or 2%, e.g., up to 0.5%,silicon; up to 2%, e.g., 0.05 to 1%, zirconium; up to 1%, e.g., 0.001 to0.1%, boron; up to 4%, e.g., 0.5 to 3%, hafnium; up to about 25 volumepercent, e.g., 0.05 to 10% by volume, of a refractory dispersoid such asyttria, lanthana, thoria, etc.; and at least one metal from the groupconsisting of nickel, cobalt and iron, preferably in an amount of atleast 25 or Since nitrogen can have a positive processing effect, anitrogen level of at least 0.001%, preferably at least 0.01%, and up to0.075% is considered beneficial in such superalloy compositions.

The attributes of alloys within the invention are deemed all the moresurprising from structural stability considerations. By way ofexplanation conventional wrought and cast superalloys are normally proneto sigma phase formation in respect of highly alloyed nickel-chromiumbase alloy compositions having an electron vacancy number, N,., equal toor greater than about 2.26 to 2.41. Sigma, of course, is rathersynonymous with short term structural stability. Yet, alloys within theinvention when mechanically alloyed have shown virtually no loss in roomtemperature ductility after being heat treated (aged) for 2000 hours at1500F., this obtaining notwithstanding N, values ranging from 2,39 to2.59. For example, Alloy C had an N,. number of 2.57, well above the2.26-2.41 range. Metallographic examination did not reveal the presenceof sigma. It is believed that mechanical alloying is largely, if notcompletely, responsible for this phenomenon.

It might be further added that despite the levels of oxidation andsulfidation resistance attainable in accordance herewith, the artisanmay wish, as is not uncommon, to provide the alloys with a corrosionresistant coating of aluminum or an alloy containing aluminum andchromium. Even if this be the case, should the coating be ruptured orotherwise penetrated alloys of the instant invention are markedlycapable of retarding further corrosion attack.

Although the invention has been described in con nection with preferredembodiments, modifications may be resorted to without departing from thespirit and scope of the invention, as those skilled in the art willreadily understand. Such are considered within the purview and scope ofthe invention and appended claims.

We claim:

1. A mechanically alloyed dispersion strengthenable, precipiationhardenable powder consisting essentially of about 13 to 17% chromium,about 2.5 to 6% aluminum, about 2 to 4.25% titanium, about 1.75 to 4.5%molybdenum, about 3.75 to 6.25% tungsten, about 0.02 to 0.5% zirconium,about 0.001 to 0.025% boron, yttria in a small but effective amount toenhance high temperature strength characteristics, up to 4% tantalum, upto 0.2% carbon and the balance essentially nickel.

2. An alloy in accordance with claim 1 characterized by arnicrostructure having coarse elongated grains.

3. An alloy in accordance with claim 1 containing 13.25 to 16.25%chromium, 2.75 to 5.25% aluminum, 2 to 4.25% titanium, 1.75 to 4.25%molybdenum, about 3.75 to 6.25% tungsten, about 0.05 to 0.175%zirconium, about 0.001 to 0.022% boron, about 0.5 to 2% yttria, up to 3%tantalum, up to about 0.125% carbon and the balance essentially nickel.

4. An alloy in accordance with claim 1 containing about 13.75 to 16.25%chromium, about 3.5 to 5.25% aluminum and about 2 to 3% titanium, saidalloy being characterized by a high degree of oxidation resistance atelevated temperature levels.

5. An alloy in accordance with claim 1 containing about 13.75 to 16.25%chromium, about 2.75 to about 4.6% aluminum and about 4.75 to about6.25% tungsten, said alloy being characterized by good sulfidationresistance at elevated temperatures.

6. An alloy in accordance with claim 5 in which the sum of titanium plustungsten is at least 7.75%.

7. An alloy in accordance with claim 6 in which the said sum is at least8.5%.

8. An alloy in accordance with claim 1 containing about 13.75 to 16.25%chromium, about 3.5 to 5.25% aluminum, about 2.4 to about 3.25%titanium, about 1.75 to 4.25% molybdenum, about 4.75 to 6.25% tungsten,about 0.05 to 0.175% zirconium, about 0.001 to 0.022% boron, about 0.4to 2% yttria, up to 0.125% carbon and the balance essentially nickel.

9. An alloy in accordance with claim 8 containing 0.5 to 1.5% yttria andup to 3% tantalum.

10. An alloy made up of metallic powders consisting essentially of about13% to 17% chromium, about 2.5 to 6% aluminum, about 2 to 4.25%titanium, about 1.75 to 4.5% molybdenum. about 3.75 to 6.25% tungsten,about 0.02 to 0.5% zirconium, about 0.001 to 0.025% boron, about 0.2 to2% yttria, up to 4% tantalum, up to 0.2% carbon. up to 10% cobalt. up to3% 10 about 3.75 to 6.25% tungsten, about 0.02 to 0.5% zirconium, about0.00l to 0.025% boron, yttria in a small but effective amount to enhancestrength characteristics, up to 4% tantalum, up to 0.2% carbon and thebalance essentially nickel.

12. An alloy in accordance with claim 11 in which the nitrogen does notexceed about 0.075%.

* t t I

1. A MECHANICALLY ALLOYED DISPERSION STRENGTHENABLE, PRECIPIATIONHARDENABLE POWDER CONSISTING ESSENTIALLY OF ABOUT 13 TO 17% CHROMIUM,ABOUT 2.5 TO 6% ALUMINUM, ABOUT 2 TO 4.25% TITANIUM, ABOUT 1.75 TO 4.5%MOLYBDENUM, ABOUT 3.75 TO 6.25% TUNGSTEN, ABOUT 0.02 TO 0.5% ZIRCONIUM,ABOUT 0.001 TO 0.025% BORON, YTTRIA IN A SMALL BUT EFFECTIVE AMOUNT TOENHANCE HIGH TEMPERATURE STRENGTH CHARACTERISTIS, UP TO 4% TANTALUM, UPTO 0.2% CARBON AND THE BALANCE ESSENTIALLY NICKEL.
 2. An alloy inaccordance with claim 1 characterized by a microstructure having coarseelongated grains.
 3. An alloy in accordance with claim 1 containing13.25 to 16.25% chromium, 2.75 to 5.25% aluminum, 2 to 4.25% titanium,1.75 to 4.25% molybdenum, about 3.75 to 6.25% tungsten, about 0.05 to0.175% zirconium, about 0.001 to 0.022% boron, about 0.5 to 2% yttria,up to 3% tantalum, up to about 0.125% carbon and the balance essentiallynickel.
 4. An alloy in accordance with claim 1 containing about 13.75 to16.25% chromium, about 3.5 to 5.25% aluminum and about 2 to 3% titanium,said alloy being characterized by a high degree of oxidation resistanceat elevated temperature levels.
 5. An alloy in accordance with claim 1containing about 13.75 to 16.25% chromium, about 2.75 to about 4.6%aluminum and about 4.75 to about 6.25% tungsten, said alloy beingcharacterized by good sulfidation resistance at elevated temperatures.6. An alloy in accordance with claim 5 in which the sum of titanium plustungsten is at least 7.75%.
 7. An alloy in accordance with claim 6 inwhich the said sum is at least 8.5%.
 8. An alloy in accordance withclaim 1 containing about 13.75 to 16.25% chromium, about 3.5 to 5.25%aluminum, about 2.4 to about 3.25% titanium, about 1.75 to 4.25%molybdenum, about 4.75 to 6.25% tungsten, about 0.05 to 0.175%zirconium, about 0.001 to 0.022% boron, about 0.4 to 2% yttria, up to0.125% carbon and the balance essentially nickel.
 9. An alloy inaccordance with claim 8 containing 0.5 to 1.5% yttria and up to 3%tantalum.
 10. An alloy made up of metallic powders consistingessentially of about 13% to 17% chromium, about 2.5 to 6% aluminum,about 2 to 4.25% titanium, about 1.75 to 4.5% molybdenum, about 3.75 to6.25% tungsten, about 0.02 to 0.5% zirconium, about 0.001 to 0.025%boron, about 0.2 to 2% yttria, up to 4% tantalum, up to 0.2% carbon, upto 10% cobalt, up to 3% columbium, up to 3% hafnium, up to 0.3%nitrogen, up to about 1% oxygen, up to 3% iron and the balance nickel.11. A dispersion-strengthened mechanically alloyed superalloy powderconsisting essentially of nitrogen present in an amount up to 0.1% andfrom 13 to 17% chromium, about 2.5 to 6% aluminum, about 2 to 4.25%titanium, about 1.75 to 4.5% molybdenum, about 3.75 to 6.25% tungsten,about 0.02 to 0.5% zirconium, about 0.001 to 0.025% boron, yttria in asmall but effective amount to enhance strength characteristics, up to 4%tantalum, up to 0.2% carbon and the balance essentially nickel.
 12. Analloy in accordance with claim 11 in which the nitrogen does not exceedabout 0.075%.